Asymmetric allylboration of aldehydes has been an invaluable tool for the formation of carbon-carbon bonds with control over relative and absolute stereochemistry (Lachance, H.; Hall, D. G. Org. React. 2008, 73, 1; Denmark, S. E.; Fu, J. Chem. ReV. 2003, 103, 2763; Denmark, S. E.; Almstead, N. G. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH: Weinheim, Germany, 2000; Chapter 10, p 299; Chemler, S. R.; Roush, W. R. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH: Weinheim, Germany, 2000; p 403; Yamamoto, Y.; Asao, N. Chem. ReV. 1993, 93, 2207; Roush, W. R. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, U.K., 1991; Vol. 2, p 1). The foundation of this reaction was provided by Hoffmann's recognition of the diastereospecificity of the reaction when both (E)- and (Z)-crotylboronates are used (Hoffmann, R. W.; Ladner, W. Tetrahedron Lett. 1979, 20, 4653; Hoffmann, R. W.; Zeiss, H. J. Angew. Chem., Int. Ed. Engl. 1979, 18, 306; Hoffmann, R. W.; Zeiss, H. J. J. Org. Chem. 1981, 46, 1309) and Brown's highly stereoselective allylborations using pinene-derived chiral reagents (Brown, H. C.; Jadhav, P. K. J. Am. Chem. Soc. 1983, 105, 2092.; Brown, H. C.; Bhat, K. S. J. Am. Chem. Soc. 1986, 108, 293. (f) Ramachandran, P. V. Aldrichimica Acta 2002, 35, 23). Over the past three decades, additional methodologies that have relied upon stoichiometric chiral reagents or mediators have included work by Roush (Roush, W. R.; Walts, A. E.; Hoong, L. K. J. Am. Chem. Soc. 1985, 107, 8186; Chen, M.; Handa, M.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14602; Kister, J.; DeBaillie, A. C.; Lira, R.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14175), Masamune (Short, R. P.; Masamune, S. J. Am. Chem. Soc. 1989, 111, 1892), Corey (Corey, E. J.; Yu, C. M.; Kim, S. S. J. Am. Chem. Soc. 1989, 111, 5495), Seebach (Seebach, D.; Beck, A. K.; Imwinkelzied, R.; Roggo, S.; Wonnacott, A. Helv. Chim. Acta 1987, 70, 954), Duthaler (Riediker, M.; Duthaler, R. O. Angew. Chem., Int. Ed. Engl. 1989, 28, 494), Panek (Panek, J. S.; Yang, M. J. Am. Chem. Soc. 1991, 113, 6594), Leighton (Kinnaird, I. W. A.; Ng, P. Y.; Kubota, K.; Wang, X.; Leighton, J. L. J. Am. Chem. Soc. 2002, 124, 7920; Hackman, B. M.; Lombardi, P. J.; Leighton, J. L. Org. Lett. 2004, 6, 4375.), Chong (Wu, T. R.; Shen, L.; Chong, J. M. Org. Lett. 2004, 6, 2701), Soderquist (Burgos, C. H.; Canales, E.; Matos, K.; Soderquist, J. A. J. Am. Chem. Soc. 2005, 127, 8044. (m) Gonzalez, A. Z.; Roman, I. G.; Alicea, E.; Canales, E.; Soderquist, J. A. J. Am. Chem. Soc. 2009, 131, 1269), and Aggarwal (Althaus, M.; Mahmood, A.; Suarez, J. R.; Thomas, S. P.; Aggarwal, V. K. J. Am. Chem. Soc. 2010, 132, 4025).
Catalytic methods that avoid the use of stoichiometric chiral reagents have also emerged, and include work by Yamamoto (Furuta, K.; Mouri, M.; Yamamoto, H. Synlett 1991, 561), Umani-Ronchi (Costa, A. L.; Piazza, M. G.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. J. Am. Chem. Soc. 1993, 115, 7001), Keck (Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am. Chem. Soc. 1993, 115, 8467), Denmark (Denmark, S. E.; Fu, J. Chem. ReV. 2003, 103, 2763; Denmark, S. E.; Fu, J. J. Am. Chem. Soc. 2001, 123, 9488) and others (Malkov, A.; Orsini, M.; Pernazza, D.; Muir, K. W.; Langer, V.; Meghani, P.; Kocovsky, P. Org. Lett. 2002, 4, 1047; Kim, I. S.; Ngai, M.; Krische, M. J. J. Am. Chem. Soc. 2008, 130, 14891). Also, recent catalytic allylborations by Hall (Kennedy, J. W. J.; Hall, D. G. J. Am. Chem. Soc. 2002, 124, 11586; Rauniyar, V.; Hall, D. G. J. Am. Chem. Soc. 2004, 126, 4518; Yu, S. H.; Ferguson, M. J.; McDonald, R.; Hall, D. G. J. Am. Chem. Soc. 2005, 127, 12808; Rauniyar, V.; Hall, D. G. Angew. Chem., Int. Ed. 2006, 45, 2426; Hall, D. G. Synlett 2007, 1644; Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481; Rauniyar, V.; Hall, D. G. J. Org. Chem. 2009, 74, 4236), Miyaura (Ishiyama, T.; Ahiko, T.-A.; Miyaura, N. J. Am. Chem. Soc. 2002, 124, 12414), Shibasaki (Wada, R.; Oisaki, K.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2004, 126, 8910), and Schaus (Lou, S.; Moquist, P. N.; Schaus, S. E. J. Am. Chem. Soc. 2006, 128, 12660; Barnett, D. S.; Moquist, P. N.; Schaus, S. E. Angew. Chem., Int. Ed. 2009, 48, 8679) have opened new doors for the synthesis of homoallylic alcohols. Most of the current methods for enantioselective propargylations involve the use of chiral reagents (Ikeda, N.; Arai, I.; Yamamoto, H. J. Am. Chem. Soc. 1986, 108, 483-486; Haruta, R.; Ishiguro, M.; Ikeda, N.; Yamamoto, H. J. Am. Chem. Soc. 1982, 104, 7667-7669; Corey, E. J.; Yu, C.-M.; Lee, D.-H. J. Am. Chem. Soc. 1990, 112, 878-879; Lee, K.-C.; Lin, M,-J.; Loh, T.-P. Chem. Commun. 2004, 2456-2457; Lai, C.; Soderquist, J. A. Org. Lett. 2005, 7, 799-802). Alternatives to propargylation involving stoichiometric chiral reagents have also been developed and are limited to use of allenylic or propargylic metal reagents or intermediates (Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763; Boldrini, G. P.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. J. Chem. Soc., Chem. Commun. 1986, 685-686; Minowa, N.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1987, 60, 3697-3704; Keck, G. E.; Krishnamurthy, D.; Chen, X. Tetrahedron Lett. 1994, 35, 8323-8324; Yu, C.-M.; Yoon, S.-K.; Choi, H.-S.; Baek, K. Chem. Commun. 1997, 763-764; Yu, C.-M.; Yoon, S.-K.; Baek, K.; Lee, J.-Y. Angew. Chem. Int. Ed. 1998, 37, 2392-2395; Iseki, K.; Kuroki, Y.; Kobayashi, Y. Tetrahedron: Asymmetry, 1998, 9, 2889-2894; Denmark, S. E.; Wynn, T. J. Am. Chem. Soc. 2001, 123, 6199-6200; Evans, D. A.; Sweeney, Z. K.; Rovis, T.; Tedrow, J. S. J. Am. Chem. Soc. 2001, 123, 12095-12096; Hanawa, H.; Uraguchi, D.; Konishi, S.; Hashimoto, T.; Maruoka, K. Chem.-Eur. J. 2003, 9, 4405-4413; Inoue, M.; Nakada, M. Org. Lett. 2004, 6, 2977-2980; Naodovic, M.; Xia, G.; Yamamoto, H. Org. Lett. 2008, 10, 4053-4055; Fandrick, D. R.; Fandrick, K. R.; Reeves, J. T.; Tan, Z.; Tang, W.; Capacci, A. G.; Rodriguez, S.; Song, J. J.; Lee, H.; Lee, H.; Yee, N. K.; Senanayake, C. H. J. Am. Chem. Soc. 2010, 132, 7600-7601; Usanov, D. L.; Yamamoto, H. Angew. Chem. Int. Ed. 2010, 49, 8169-8172; Shi, S.-L.; Xu L.-W.; Oisaki, K.; Shibasaki, M. J. Am. Chem. Soc. 2010, 132, 6638-6639).
Enantiomerically pure homopropargylic alcohols are highly useful intermediates and have shown a broad synthetic utility. The terminal alkyne functionality serves as a synthetic handle for coupling reactions, metathesis and heterocycle synthesis (Trost, B. M.; Dumas, J.; VIIIa, M. J. Am. Chem. Soc. 1992, 114, 9836-9845; McDonald, F. E.; Gleason, M. M. J. Am. Chem. Soc. 1996, 118, 6648; Schmidt, D. R.; O'Malley, S. J.; Leighton, J. L. J. Am. Chem. Soc. 2003, 125, 1190-1191; O'Sullivan, P. T.; Buhr, W.; Fuhry, M. A. M.; Harrison, J. R.; Davies, J. E.; Feeder, N.; Marshall, D. R.; Burton, J. W.; Holmes, A. B. J. Am. Chem. Soc. 2004, 126, 2194-2207; Trost, B. M.; Dong, G. Nature, 2008, 456, 485-488; Francais, A.; Leyva, A.; Etxebarria-Jardi, G. Ley, S. V. Org. Lett. 2010, 12, 340-343). The addition of allenic or propargylic reagents to carbonyl compounds is mechanistically similar to the corresponding reaction with the allylic reagents. However, though many useful and innovative methods exist for the synthesis of homoallylic alcohols (Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763; Brown, H. C.; Jadhav, P. K. J. Am. Chem. Soc. 1983, 105, 2092; Corey, E. J.; Yu, C. M.; Kim, S. S. J. Am. Chem. Soc. 1989, 111, 5495; Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am. Chem. Soc. 1993, 115, 8461; Burgos, C. H.; Canales, E.; Matos, K.; Soderquist, J. A. J. Am. Chem. Soc. 2005, 127, 8044.; Lachance, H.; Hall, D. G. Org. React. 2008, 73, 1; Chen, M.; Handa, M.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14602; Althaus, M.; Mahmood, A.; Suarez, J. R.; Thomas, S. P.; Aggarwal, V. K. J. Am. Chem. Soc. 2010, 132, 4025), the enantioselective synthesis of homopropargylic alcohols still remains a challenge. There are two main issues: the lower reactivity of the allenylic and propargylic substrates in comparison to allylic reagents, and the difficulties associated with controlling the regioselectivity (H. Yamamoto, in Comprehensive Organic Synthesis: Propargyl and Allenyl Organometallics, ed. C. H. Heathcock, Pergamon, Oxford, 1991, vol. 2, pp. 81-98).
However, most stereoselective methods are limited by one or more drawbacks. These include the use of stoichiometric chiral inductors, allylation reagents that are difficult to prepare or are air/moisture-sensitive, the use of undesirable metal-based catalysts such as tin, or substrates leading to toxic byproducts. Therefore, what is needed is a competent, catalytic, and practical solution for the direct enantioselective synthesis of homoallylic alcohols, an important class of versatile intermediates used in the synthesis of pharmaceuticals and natural products.